000
FOUS11 KWBC 252136
QPFHSD
PROBABILISTIC HEAVY SNOW AND ICING DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
436 PM EST WED FEB 25 2015
VALID 00Z THU FEB 26 2015 - 00Z SUN MAR 01 2015
...SOUTHERN APPALACHIANS/SOUTHEAST/MID-ATLANTIC...
PERHAPS ONE OF THE MORE PRONOUNCED SRN STREAM SHORT WAVE TROUGHS
IN RECENT MEMORY IS SLIDING ACROSS THE SRN TIER OF THE COUNTRY
THIS AFTN. WATER VAPOR IMAGERY SHOWS QUITE A WELL-DEFINED
BAROCLINIC LEAF AND THIS FEATURE IS CAPITALIZING ON A SLIGHT
ANOMALOUS INFLUX OF GULF OF MEXICO MOISTURE... AS A WIDESPREAD
ARRAY OF PRECIP IS OCCURRING FROM THE ARKLATEX EAST INTO PARTS OF
THE SOUTHEAST. THE UPPER-LEVEL SHORT WAVE IS EXPECTED TO PRESS
DOWNSTREAM RAPIDLY OVER THE NEXT 24 HRS... AS A SURFACE WAVE
DEVELOPS JUST SOUTH OF THE FL PANHANDLE IN THE NERN GULF AND CLIP
THE OUTER BANKS OF NC BEFORE PRESSING RAPIDLY DOWNSTREAM INTO THE
ATLANTIC. THE GUIDANCE INDICATES VERY NARROW SPREAD AT 500MB AND
THE SURFACE LOW ON THE PROGRESSION AND AMPLITUDE OF THE STORM
SYSTEM BUT A CONTINUED SUBTLE TREND TO THE NORTH WITH MOISTURE
CONTINUES TO HINDER THE ALREADY COMPLEX FCST. WPC FOLLOWED A BLEND
OF THE GFS/ECMWF ON HEAVY SNOW AXIS MAINLY PRODUCED BY STRONG
DYNAMIC COOLING ON THE NWRN QUAD OF THE PRECIP SHIELD OR NEAR THE
TRACK OF THE 850/700MB LOW. THIS STILL SUGGESTS A HEAVY SNOW AXIS
FROM NERN GA OR EXTREME UPSTATE SC TO SERN VA... INCLUDING CLT/RDU
METRO AREAS. IN FACT... WPC WENT WITH 4 TO 12 INCH HEAVY SNOW
PROBS ALONG THIS CORRIDOR. PTYPE REMAINS AN ISSUE THOUGH ON THE
SERN FRINGE OF THE SNOW AXIS ACROSS ERN NC INTO PERHAPS SC AND WPC
WENT WITH A LOW PROB OF A MIX/ICE/SLEET. THE OTHER TOUGH PART OF
THE FCST IS HOW FAR NORTH TO EXTEND THE HEAVY SNOWFALL AXIS ACROSS
SERN VA/EXTREME SRN MD AND THE SNOW POSSIBILITIES FROM THE MAJOR
METRO CENTERS FROM DC TO PHL WITH THE GUIDANCE EDGING NORTHWARD.
WPC BROUGHT A LOW PROB OF 4 INCHES INTO THE DC/BWI AREAS FOR TMRW
MORNING BUT NOT INTO SERN PA.
...MO VALLEY TO MID MS VALLEY DAY 1...
AN 850-700 MB WAVE MOVING THROUGH THE MID MS VALLEY WILL GRADUALLY
BEGIN TO FILL WHILE HEADING INTO THE OH/TN VALLEYS BUT BEFORE THEN
EXPECT LOCALIZED HEAVY SNOWFALL FROM NORTH CENTRAL IL INTO SERN
IA/NERN MO. WPC WENT WITH A BLEND OF THE GUIDANCE FOR THE HEAVY
SNOW PROBS.
...WEST...
AN EXTENDED PERIOD OF HEAVY SNOW IS POSSIBLE FOR THE CO/SRN
ROCKIES OVER THE NEXT THREE DAYS WITH AN INCREASING THREAT ACROSS
AN EXTENSIVE PART OF THE WRN TERRAIN ON FRI AND SAT. THE MAIN
THREAT ON THURS WILL BE IN ASSOCIATION WITH WEAK UPPER DYNAMICS
DIVING THROUGH THE FOUR CORNERS REGION INTO THE SRN PLAINS...
WHILE WEDGING ARCTIC HIGH PRESSURE EXTENDS DOWN THE ENTIRE FRONT
RANGE OF THE ROCKIES. HEAVY UPSLOPE FLOW OVER NERN NM/ERN CO
SHOULD RESULT IN HEAVY OROGRAPHIC SNOWFALL FOR THE EAST FACING
TERRAIN... ESPECIALLY FOR THE SANGRE DE CRISTO RANGE. THEN ON FRI
AND SAT... TREMENDOUS UPPER HEIGHT FALLS AND A POWERFUL DIGGING
UPPER JET WILL HELP ESTABLISH A SEPARATION OF STREAMS AND CLOSED
LOW FORMING OVER NV/CA BY THE END OF THE FCST PERIOD. ARCTIC HIGH
PRESSURE WILL BEGIN TO EXPAND INTO THE INTER-MOUNTAIN WEST...
WHILE FAVORABLE SWRLY UPPER DIFLUENT FLOW AHEAD OF THE DIGGING
TROUGH SHOULD BE IDEAL FOR HEAVY SNOW FROM THE NW/SRN ROCKIES ON
FRI AND SIERRA/NV TERRAIN TO THE CO/SRN ROCKIES ON SAT. THE AREA
OR MTN RANGE MOST LIKELY TO SEE VERY HEAVY SNOWFALL WILL BE IN
SWRN CO ACROSS THE SAN JUANS. OVERALL WPC STAYED CLOSELY TO THE
GFS/ECMWF FOR THE PATTERN CHANGE AND HEAVY SNOW PROBS FOR THE WRN
TERRAIN.
MUSHER
$$